As the needs of fiberglass reinforced resinous articles and sheets become more specialized, the properties of the reinforcing mats of glass filaments have become more highly engineered. For example, mats comprised of continuous glass filaments for use in stampable thermoplastics required the ability to "flow" with the resin in the stamping operation to provide adequate reinforcement throughout the article. Some of the previous mat-producing systems even go so far as to first produce a mat of a plurality of layers of continuous glass filaments and then needlepunch the mat to, first, mechanically bond the mat together and, secondly, "break" the filaments to render the mat useful for reinforcing resinous sheets that are to be stamped. For example, see U.S. Pat. Nos. 3,883,333 and 4,277,531.
According to the '531 patent, the broken filaments move with the resin during the stamping operation to ensure that the resin flowing to the ends of the mold is properly reinforced with glass. Unfortunately, mats of such "chopped or severed" strands are generally not as strong as those produced from continuous strands. In an example set forth in that patent, it was specified that there be over 500 needle penetrations, by a barbed needle, per square inch. Clearly, the damage to the previously continuous strands will be rather severe.
On the other hand, continuous strand mats produced according to the principles set forth in U.S. Pat. Nos. 3,295,942; 3,854,917 and 3,969,171 also find utility for use in producing printed circuit boards. Such printed circuit boards are generally comprised of a continuous strand mat of glass fibers and a thermosetting resin, such as polyester. One of the requirements of printed circuit boards is that they have good "punchability" to permit clean holes to be punched in the boards for installation of appropriate electrical terminations and/or fittings.
The present invention provides a mat capable of satisfying the requirements of "punchability" as well as "flowability" for use in printed circuit boards and stampable tbermoplastics, respectively.